OverlayFS Sees Many Fixes Thanks To AI Code Review

Merged this weekend for Linux 7.4 and also marked for back-porting to current stable kernel versions are a number of fixes to the OverlayFS union mount file-system. OverlayFS changes for Linux 7.4 just consist of many fixes, including some with security implications. These fixes are marked for back-porting to the stable Linux kernel versions too. Chris Mason of Btrfs notoriety and who has recently been focused on AI/LLM driven code review for the Linux kernel ended up uncovering a number of OverlayFS bugs. Amir Goldstein explained in the pull request of the OverlayFS updates: "- Fixes for bugs found by Chris Mason's AI review, several of them reachable by unprivileged users: an info leak, use-after-free and NULL deref bugs, an RCU walk stall with remote layers and data loss with nfs_export - Fix copy up of files with an empty security.capability xattr, which any user could set to block copy up - Fix a regression from v6.16 with the override_creds mount option - Two casefold fixes" There ended up being more than a dozen patches to OverlayFS in the past week from Chris Mason after uncovering these issues in the code. With the information leak, UAF, and related bugs reachable by unprivileged users there are security considerations. These OverlayFS fixes merged ahead of Linux 7.4-rc1 and to be back-ported to stable branches in the coming days can be found via this Git merge.